1. Field of the Invention
The present application relates to a light emitting diode (LED) package, and more particularly to an LED package having favorable reliability and water resistance.
2. Description of Related Art
Due to advantages of long lifetime, small volume, great resistance to vibration, low heat emission, and low power consumption, LEDs have been extensively applied in various home appliances and instruments as indicators or light sources. With recent development towards multicolor and high illumination, the applications of the LEDs are extended to large-sized outdoor billboards, traffic lights, and so forth. In the future, the LEDs are likely to become power-saving and environment-protecting light sources in replacement of tungsten filament lamps and mercury vapor lamps.
In a conventional white LED package, LED chips emitting light beams with different light-emitting wavelengths are normally used together with different phosphor powder, such that the light beams can be mixed to generate the white light. Nonetheless, since the phosphor powder absorbs water, phosphor is apt to be hydrolyzed or oxidized. Namely, a reflective layer is reacted with moisture, which results in deterioration of the reflective layer. Accordingly, luminance of the white LED package is reduced, and color of light is not uniform. To prevent the moisture from entering into the package, silica gel or resin with relatively high density can be employed to package the LED. However, the comparatively dense silica gel or resin often has great hardness. Therefore, during a packaging process, conductive bonding wires within the package are prone to be broken, thus reducing yield of products.
FIG. 1 is a schematic view illustrating measured results of corresponding light-emitting intensities and time of a conventional LED package in a high temperature and moisture environment. FIG. 2 is a schematic view illustrating measured results of corresponding chromo-coordinates and time of a conventional LED package in a high temperature and moisture environment. Referring to FIG. 1, the conventional LED package is a package structure containing an LED chip and phosphor powder. Light-emitting intensities of the conventional LED package in different time points are measured when the temperature is at 60° C. and the relative humidity (RH) is 90%. The measured results show that the light-emitting intensities of the conventional LED package are reduced along with time in the high temperature and moisture environment. Besides, referring to FIG. 2, chromo-coordinates of the conventional LED package are measured in a 60° C. and 90% RH environment. Likewise, it is shown that drift chromo-coordinates X and Y are obtained from the measurement of time.